U.S. patent application number 12/226390 was filed with the patent office on 2009-04-23 for method of metering process additives, in particular antistics, into polymerization reactors.
This patent application is currently assigned to Basell Polyolefine GmbH. Invention is credited to Manfred Hecker, Rainer Karer, Shahram Mihan.
Application Number | 20090105414 12/226390 |
Document ID | / |
Family ID | 38580046 |
Filed Date | 2009-04-23 |
United States Patent
Application |
20090105414 |
Kind Code |
A1 |
Mihan; Shahram ; et
al. |
April 23, 2009 |
METHOD OF METERING PROCESS ADDITIVES, IN PARTICULAR ANTISTICS, INTO
POLYMERIZATION REACTORS
Abstract
Method for metering polar, antistatically acting process
auxiliaries into a polymerization reactor in which the process
auxiliaries are present in solution in a nonpolar solvent, wherein
the electrical conductivity of the solution is measured and the
amount of the process auxiliary metered in is determined from the
electrical conductivity.
Inventors: |
Mihan; Shahram; (Bad Soden,
DE) ; Karer; Rainer; (Kaiserslautern, DE) ;
Hecker; Manfred; (Neustadt Wied, DE) |
Correspondence
Address: |
LyondellBasell Industries
3801 WEST CHESTER PIKE
NEWTOWN SQUARE
PA
19073
US
|
Assignee: |
Basell Polyolefine GmbH
Wesseling
DE
|
Family ID: |
38580046 |
Appl. No.: |
12/226390 |
Filed: |
May 4, 2007 |
PCT Filed: |
May 4, 2007 |
PCT NO: |
PCT/EP2007/003943 |
371 Date: |
October 17, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60813235 |
Jun 13, 2006 |
|
|
|
Current U.S.
Class: |
525/51 ;
526/74 |
Current CPC
Class: |
C08F 210/16 20130101;
C08F 210/16 20130101; C08F 210/16 20130101; C08F 10/00 20130101;
C08F 210/16 20130101; C08F 10/00 20130101; B01J 2219/00254
20130101; B01J 8/1809 20130101; B01J 19/002 20130101; C08F 210/16
20130101; B01J 2208/00734 20130101; B01J 2219/00247 20130101; C08F
210/06 20130101; C08F 110/02 20130101; C08F 210/16 20130101; C08F
210/08 20130101; C08F 2/005 20130101; C08F 210/14 20130101; C08F
2/005 20130101; C08F 2/44 20130101 |
Class at
Publication: |
525/51 ;
526/74 |
International
Class: |
C08F 2/06 20060101
C08F002/06 |
Foreign Application Data
Date |
Code |
Application Number |
May 11, 2006 |
DE |
10 2006 022 256.3 |
Claims
1. A method for metering polar, antistatically acting process
auxiliaries into a polymerization reactor in which the process
auxiliaries are present in solution in a nonpolar solvent, wherein
the electrical conductivity of the solution is measured and the
amount of the process auxiliary metered in is determined from the
electrical conductivity, the antistatically acting process
auxiliary being a chemical compound or a mixture of chemical
compounds which has an electrical conductivity of at least 0.05
.mu.S/cm and the nonpolar solvent being a solvent having an
electrical conductivity of not more than 0.01 .mu.S/cm.
2. The method according to claim 1, wherein ethylene is
homopolymerized or ethylene is copolymerized with 1-butene,
1-hexene or 1-octene.
3. The method according to claim 1, wherein propylene is
homopolymerized or propylene is copolymerized with ethylene,
1-butene, 1-hexene or 1-octene.
4. The method according to claim 1, wherein the polymerization
reactor comprises a gas-phase fluidized bed.
5. The method according to claim 1, wherein the amount of the
solution comprising the process auxiliary which is metered into the
reactor per unit time is measured.
6. The method according to claim 5, wherein the measured amount of
process auxiliary is compared with a set value and, in the case of
deviations, the flow of the solution comprising the process
auxiliary is adjusted.
7. The method according to claim 1, wherein the process auxiliary
has an electrical conductivity of at least 0.1 .mu.S/cm, in
particular at least 0.5 .mu.S/cm.
8. The method according to claim 1, wherein the solvent has an
electrical conductivity of not more than 10.sup.-3 .mu.S/cm, in
particular not more than 10.sup.-4 .mu.S/cm.
9. The method according to claim 1, wherein the antistatically
acting compound comprises a functional group selected from among
--OH, --COOH, --NH.sub.2, --NHR.sup.1--SH, --PH.sub.2, --PHR.sup.1
and --SO.sub.3H, where R.sup.1 is an alkyl, aryl, alkylaryl or
arylalkyl radical in which one or more carbon atoms may also be
replaced by heteroatoms.
10. The method according to claim 1, wherein the antistatically
acting compound comprises a polysulfone copolymer, a polymeric
polyamine and an oil-soluble sulfonic acid.
11. A process for the polymerization of unsaturated monomers, in
particular 1-olefins, using the metering method according to claim
1.
Description
[0001] The invention relates to a method of for metering polar,
antistatically acting process auxiliaries into a polymerization
reactor in which the process auxiliaries are present in solution in
a nonpolar solvent.
[0002] In continuous gas-phase polymerization, antistatics are used
to avoid electrostatic charging. Antistatically acting process
auxiliaries generally comprise organic compounds having polar
functional groups such as acid or ester groups, amine or amide
groups or hydroxyl or ether groups. Examples of constituents of
typical antistatics are polysulfone copolymers, polymeric
polyamines, oil-soluble sulfonic acids or polysiloxanes.
[0003] In olefin polymerization, dilute solutions of the
antistatics are generally metered in order to avoid polymer
deposits on the reactor wall and lump formation. Concentration
fluctuations can occur in the solutions as a result of, for
example, the effect of cold, aging phenomena, incomplete
homogenization of the solution, precipitation of one or more of the
components or simply as a result of a batch change. In the case of
relatively large fluctuations, operational malfunctions through to
plant shutdowns can occur.
[0004] To avoid electrostatic charges and the process engineering
problems associated therewith, the electrostatic charges are
monitored in gas-phase polymerization reactors by means of
electrostatic sensors in order to be able to undertake
countermeasures in good time. However, in the case of relatively
high charging, the sensors alone are not able to determine whether
fluctuations in the introduction of antistatically active process
auxiliaries or other causes are responsible for this.
[0005] It was therefore an object of the invention to overcome the
abovementioned disadvantages of the prior art and to provide a
method which allows more uniform metering and monitoring of process
auxiliaries, in particular antistatics.
[0006] The invention provides a method of the abovementioned type
in which the electrical conductivity of the solution is measured
and the amount of the process auxiliary metered in is determined
from the electrical conductivity.
[0007] The measurement of the conductivity of the solution allows
the content of antistatic in the solution to be determined in a
simple manner and thus enables the amount introduced into the
polymerization reactor to be controlled.
[0008] For the purposes of the present invention, a polar
antistatically acting process auxiliary is a chemical compound or a
mixture of chemical compounds which has an electrical conductivity
of at least 0.05 .mu.S/cm and is able to reduce negative or
positive electrostatic charges in the reactor. The process
auxiliary preferably has an electrical conductivity of at least
0.10 .mu.S/cm, more preferably at least 0.20 .mu.S/cm, more
preferably 0.50 .mu.S/cm, particularly preferably 1.0 .mu.S/cm.
[0009] Preferred antistatically acting compounds are those having a
molar mass of at least 100 g/mol, more preferably at least 150
g/mol, particularly preferably at least 200 g/mol, with mixtures
comprising at least one such antistatically acting compound also
being preferred. Further preference is given to organic
antistatically acting compounds, with those having at least 5, in
particular at least 10, carbon atoms being particularly
advantageous.
[0010] The antistatically acting compound preferably has
hydrogen-comprising functional groups selected from among --OH,
--COOH, --NH.sub.2, --NHR.sup.1, --SH, --PH.sub.2, --PHR.sup.1 and
--SO.sub.3H, where R.sup.1 is an alkyl, aryl, alkylaryl or
arylalkyl radical in which one or more carbon atoms may also be
replaced by heteroatoms.
[0011] In addition, further functional groups which do not bear any
hydrogen, e.g. --OR.sup.1, --COOR.sup.1, --SO.sub.3R.sup.1,
--SiO.sub.2R.sup.1, --NR.sup.1R.sup.2, --CHO, --CO--R.sup.1, where
R.sup.1 and R.sup.2 are each, independently of one another, an
alkyl, aryl, alkylaryl or arylalkyl radical in which one or more
carbon atoms may also be replaced by heteroatoms and the radicals
R.sup.1 and R.sup.2 may together form a ring, can preferably also
be present.
[0012] Particularly preferred process auxiliaries are those
comprising finely divided porous carbon blacks, higher polyhydric
alcohols and their ethers, for example sorbitol, polyalcohols,
polyalcohol ethers, polyvinyl alcohols, polyethylene glycols and
their ethers with fatty alcohols, anion-active substances such as
C.sub.12-C.sub.22-fatty acid soaps of alkali or alkaline earth
metals, salts of alkylsulfates of higher primary or secondary
alcohols having the general formula ROSO.sub.3M (M=alkali metal,
alkaline earth metal) or (RR')CHOSO.sub.3M, salts of mixed esters
of polyfunctional alcohols with higher fatty acids and sulfuric
acid, C.sub.12-C.sub.22-sulfonic acids or their salts of the
general formula RSO.sub.3M, alkylarylsulfonic acids or their salts,
e.g. dodecylbenzenesulfonic acid, phosphoric acid derivatives such
as di(alkoxypolyethoxyethyl)phosphates of the general formula
[RO(CH.sub.2CH.sub.2O).sub.n].sub.2POOM or phytic acid derivatives
as disclosed, for example, in EP-A 453116, cation-active
deactivators such as quaternary ammonium salts of the general
formula R.sup.1R.sup.2R.sup.3R.sup.4NX, where X is a halogen atom
and R.sup.1 to R.sup.4 are, independently of one another, an alkyl
radical, preferably one having at least 8 carbon atoms. Also
suitable are, for example, metal complexes such as the
cyanophthalocyanines disclosed in WO 93/24562.
[0013] Particularly useful process auxiliaries are nonvolatile
nitrogen-comprising compounds such as amines or amides or their
salts, in particular oligomeric or polymeric amines and amides.
Examples which may be mentioned are polyethoxyalkylamines or
polyethoxyalkylamides of the general formula
R.sup.1N[(R.sup.2O).sub.mR][(R.sup.3O).sub.nH] or
R.sup.1CON[(R.sub.2O).sub.mR][(R.sup.3O).sub.nH], where R.sup.1 to
R.sup.3 are alkyl radicals, in the case of R.sup.1 preferably alkyl
radicals having at least 8 carbon atoms, preferably at least 12
carbon atoms, and n, m are equal to or greater than 1, as described
in DE-A 31 088 43. These are also constituents of commercial
antistatics (e.g. Atmer.RTM. 163; from Uniqema). It is also
possible to use salt mixtures comprising calcium salts of
Medialanic acid and chromium salts of N-stearylanthranilic acid, as
described in DE-A 3543360, or mixtures of a metal salt of
Medialanic acid, a metal salt of anthranilic acid and a polyamine
as described in EP-A0 636 636.
[0014] Further particularly useful process auxiliaries are
polyamines or polyamine copolymers or mixtures of such compounds
with further compounds, in particular polymeric compounds. Apart
from simple polyamines such as polyvinylamine, suitable nonvolatile
polyamines are advantageously obtained from the reaction of
aliphatic primary monoamines such as n-octylamine or n-dodecylamine
or N-alkyl-substituted aliphatic diamines such as
N-n-hexadecyl-1,3-propanediamine and epichlorohydrin. These
polyaminopolyols have not only amino groups but also hydroxyl
groups. An overview of such polyamine copolymers is given in U.S.
Pat. No. 3,917,466. Polysulfone copolymers are particularly
suitable polymers for use together with polyamines or polyamine
copolymers. The polysulfone copolymers are preferably largely
unbranched and are made up of olefins and SO.sub.2 units in a molar
ratio of 1:1. 1-Decene polysulfone may be mentioned by way of
example. An overview of suitable polysulfone copolymers is also
given in U.S. Pat. No. 3,917,466.
[0015] In a particularly preferred embodiment, an antistatically
acting compound comprises a polysulfone copolymer, a polymeric
polyamine and an oil-soluble sulfonic acid. Mixtures of this type
are described, for example, in WO 00/68274 or WO 02/040554.
Preferred sulfonates are monosubstituted or disubstituted
phenylsulfonates or naphthylsulfonates.
[0016] Further antistatically acting compounds may be found in FR
2478654, U.S. Pat. No. 5,026,795, EP-A 453116, U.S. Pat. No.
4,675,368, EP-A 584574 or U.S. Pat. No. 5,391,657.
[0017] For the purposes of the present invention, a nonpolar
solvent is a solvent having a conductivity of not more than 0.01
.mu.S/cm, preferably not more than 10.sup.-3 .mu.S/cm, particularly
preferably not more than 10.sup.-4 .mu.S/cm. The conductivity of
the process auxiliary should if possible be 10 times, preferably
100 times, particularly preferably 1000 times, that of the
solvent.
[0018] The solvent can be inorganic or preferably organic.
Preference is given to C.sub.3-C.sub.20-alkanes, more preferably
C.sub.3-C.sub.12-alkanes, particularly preferably
C.sub.3-C.sub.8-alkanes.
[0019] The measurement of the conductivity of dilute solutions is
generally known. It can be carried out using customary conductivity
meters. The measuring instrument should be able to resolve
conductivities of from 10.sup.-3 to 10 .mu.S/cm.
[0020] The measurement can be carried out continuously or
discontinuously. Preference is given to a continuous measurement.
In the case of discontinuous measurement, the measurement is
preferably carried out at short intervals of not more than a few
minutes in order to ensure good monitoring.
[0021] The amount of the solution of the process auxiliary metered
into the reactor per unit time is preferably measured in parallel.
The measurement of the conductivity can in this case be carried out
in series to the flow measurement in the metering line or parallel
thereto in a bypass.
[0022] The amount of the process auxiliary metered in is determined
from the conductivity of the solution. This can be done, for
example, by simple comparison of the measured conductivity value
with previously measured conductivities of solutions of known
concentrations. When the amount of solution metered in is known,
the current amount of process auxiliary can be calculated
therefrom.
[0023] The conductivity measurement is preferably part of a
regulation of the amount of process auxiliaries metered into the
reactor per unit time. The amount of process auxiliary determined
by conductivity measurement is compared with a set value and, in
the case of deviations of the flow of the solution comprising the
process auxiliary, is adjusted up or down accordingly. The process
is particularly preferably integrated into an advanced process
controller (APC).
[0024] The metering of the process auxiliaries into the reactor can
be carried out by means of all customary methods. The process
auxiliary can be metered into the reactor separately from other
materials. However, it is preferably metered in together with other
materials having a low conductivity. It is particularly preferably
metered in together with metal alkyls and other scavengers. It can
be metered directly into the reactor or into a line leading to the
reactor.
[0025] For the purposes of the present invention, metal alkyls are
compounds of metals or semimetals with linear or cyclic alkyls
which are able to react with the active hydrogen of the
antistatics. Suitable metal alkyls are those of the general formula
(I),
M.sup.G(R.sup.1G).sub.r.sup.G(R.sup.2G).sub.s.sup.G(R.sup.3G).sub.t.sup.-
G (I)
where [0026] M.sup.G is Li, Na, K, Be, Mg, Ca, Sr, Ba, boron,
aluminum, gallium, indium, thallium, zinc, in particular Li, Na, K,
Mg, boron, aluminum or Zn, [0027] R.sup.1G is hydrogen,
C.sub.1-C.sub.10-alkyl, C.sub.6-C.sub.15-aryl, alkylaryl or
arylalkyl each having from 1 to 10 carbon atoms in the alkyl
radical and from 6 to 20 carbon atoms in the aryl radical, [0028]
R.sup.2G and R.sup.3G are each hydrogen, halogen,
C.sub.1-C.sub.10-alkyl, C.sub.6-C.sub.15-aryl, alkylaryl, arylalkyl
or alkoxy each having from 1 to 20 carbon atoms in the alkyl
radical and from 6 to 20 carbon atoms in the aryl radical, or
alkoxy with C.sub.1-C.sub.10-alkyl or C.sub.6-C.sub.15-aryl, [0029]
r.sup.G is an integer from 1 to 3 and [0030] s.sup.G and t.sup.G
are integers in the range from 0 to 2, with the sum
r.sup.G+s.sup.G+t.sup.G corresponding to the valence of M.sup.G,
with the metal alkyls usually not being identical to the activators
for the catalysts. It is also possible to use mixtures of various
metal alkyls of the formula (I).
[0031] Among the metal alkyls of the general formula (I),
preference is given to those in which [0032] M.sup.G is lithium,
magnesium, boron or aluminum and [0033] R.sup.1G is
C.sub.1-C.sub.20-alkyl.
[0034] Particularly preferred metal alkyls of the formula (I) are
methyllithium, ethyllithium, n-butyllithium, methylmagnesium
chloride, methylmagnesium bromide, ethylmagnesium chloride,
ethylmagnesium bromide, butylmagnesium chloride, dimethylmagnesium,
diethylmagnesium, dibutylmagnesium, n-butyl-n-octylmagnesium,
n-butyl-n-heptylmagnesium, in particular n-butyl-n-octylmagnesium,
tri-n-hexylaluminum, triisobutylaluminum, tri-n-butylaluminum,
triethylaluminum, dimethylaluminum chloride, dimethylaluminum
fluoride, methylaluminum dichloride, methylaluminum sesquichloride,
diethylaluminum chloride and trimethylaluminum and mixtures
thereof. The partial hydrolysis products of aluminum alkyls with
alcohols can also be used.
[0035] Most useful metal alkyls are triethylaluminum,
trimethylaluminum, trihexylaluminum and butyllithium.
[0036] The present invention further provides a process for the
polymerization of unsaturated monomers using the abovementioned
metering method.
[0037] The process is suitable, in particular, for the
polymerization of olefins and especially for the polymerization of
1-olefins (.alpha.-olefins), i.e. hydrocarbons having terminal
double bonds. Suitable monomers can be functionalized olefinically
unsaturated compounds such as ester or amide derivatives of acrylic
or methacrylic acid, for example acrylates, methacrylates, or
acrylonitrile. Preference is given to nonpolar olefinic compounds,
including aryl-substituted .alpha.-olefins. Particularly preferred
1-olefins are linear or branched C.sub.2-C.sub.12-1-alkenes, in
particular linear C.sub.2-C.sub.10-1-alkenes such as ethylene,
propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene,
1-decene or branched C.sub.2-C.sub.10-1-alkenes such as
4-methyl-1-pentene, conjugated and nonconjugated dienes such as
1,3-butadiene, 1,4-hexadiene or 1,7-octadiene or vinylaromatic
compounds such as styrene or substituted styrene. It is also
possible to polymerize mixtures of various .alpha.-olefins.
Suitable olefins also include ones in which the double bond is part
of a cyclic structure which can have one or more ring systems.
Examples are cyclopentene, norbornene, tetracyclododecene or
methylnorbornene or dienes such as 5-ethylidene-2-norbornene,
norbornadiene or ethylnorbornadiene. It is also possible to
polymerize mixtures of two or more olefins.
[0038] The process can be used in particular for the polymerization
or copolymerization of ethylene or propylene. As comonomers in
ethylene polymerization, preference is given to using
C.sub.3-C.sub.8-1-olefins, in particular 1-butene, 1-pentene,
1-hexene and/or 1-octene. Preferred comonomers in propylene
polymerization are ethylene and/or butene. Particular preference is
given to a process in which ethylene is copolymerized with 1-hexene
or 1-butene.
[0039] The polymerization of olefins can be carried out using all
customary olefin polymerization catalysts. Preference is given to
using single-site catalysts. For the purposes of the present
invention, single-site catalysts are catalysts based on chemically
uniform transition metal coordination compounds. Particularly
suitable single-site catalysts are those comprising bulky sigma- or
pi-bonded organic ligands, e.g. catalysts based on bis-cp or
mono-cp complexes, hereinafter also referred to collectively as
metallocene catalysts, or catalysts based on later transition metal
complexes, in particular iron-bisimine complexes.
[0040] Furthermore, it is also possible to use Phillips catalysts
based on chromium oxide or Ti-based Ziegler catalysts. The
preparation and use of the known catalysts in olefin polymerization
are generally known.
[0041] Preference is given to the process in combination with
hybrid catalysts. For the purposes of the present invention, hybrid
catalysts are catalyst systems which have at least two different
types of active sites derived from at least two chemically
different starting materials. The different active sites can be
active sites which are comprised in various single-site catalysts.
However, it is also possible to use active sites which are derived
from Ziegler-Natta catalysts or catalysts based on chromium, e.g.
Phillips catalysts.
[0042] Particularly preferred hybrid catalysts are those comprising
late transition metal complexes, in particular iron-bisimine
complexes, and at least one further mono-cp or bis-cp metallocene
or a Ziegler catalyst.
[0043] The process can be carried out using all industrially known
low-pressure polymerization methods at temperatures in the range
from 0 to 200.degree. C., preferably from 25 to 150.degree. C. and
particularly preferably from 40 to 130.degree. C., and under
pressures of from 0.05 to 10 MPa and particularly preferably from
0.3 to 4 MPa. The polymerization can be carried out batchwise or
preferably continuously in one or more stages. Solution processes,
suspension processes, stirred gas-phase processes and gas-phase
fluidized-bed processes are all possible. Processes of this type
are generally known to those skilled in the art. Among the
polymerization processes mentioned, gas-phase polymerization, in
particular in gas-phase fluidized-bed reactors, solution
polymerization and suspension polymerization, in particular in loop
reactors and stirred tank reactors, are preferred.
[0044] In the case of suspension polymerizations, polymerization is
usually carried out in a suspension medium, preferably in an inert
hydrocarbon such as isobutane or mixtures of hydrocarbons or else
in the monomers themselves. Suspension polymerization temperatures
are usually in the range from -20 to 115.degree. C., and the
pressure is in the range from 0.1 to 10 MPa. The solids content of
the suspension is generally in the range from 10 to 80%. The
polymerization can be carried out both batchwise, e.g. in stirring
autoclaves, and continuously, e.g. in tube reactors, preferably in
loop reactors. In particular, it can be carried out by the Phillips
PF process as described in U.S. Pat. No. 3,242,150 and U.S. Pat.
No. 3,248,179.
[0045] Suitable suspension media are all media which are generally
known for use in suspension reactors. The suspension medium should
be inert and be liquid or supercritical under the reaction
conditions and should have a boiling point which is significantly
different from those of the monomers and comonomers used in order
to make it possible for the starting materials to be recovered from
the product mixture by distillation. Customary suspension media are
saturated hydrocarbons having from 4 to 12 carbon atoms, for
example isobutane, butane, propane, isopentane, pentane and hexane,
or a mixture of these, which is also known as diesel oil.
[0046] In a further, preferred suspension polymerization process,
the polymerization takes place in a cascade of 2 or preferably 3 or
4 stirred vessels in the presence of a Ziegler catalyst. The molar
mass of the polymer fraction prepared in each of the reactors is
preferably set by addition of hydrogen to the reaction mixture. The
polymerization process is preferably carried out with the highest
hydrogen concentration and the lowest comonomer concentration,
based on the amount of monomer, being set in the first reactor. In
the subsequent further reactors, the hydrogen concentration is
gradually reduced and the comonomer concentration is altered, in
each case once again based on the amount of monomer. Ethylene or
propylene is preferably used as monomer and a 1-olefin having from
4 to 10 carbon atoms is preferably used as comonomer.
[0047] Because the Ziegler catalyst generally suffers a reduction
in its polymerization activity with rising hydrogen concentration
and because a process-related dilution of the suspension with
increasing total conversion occurs, the reacting polymer particles
in the first reactor have the longest mean residence time. For this
reason, the highest conversion of the added monomer to homopolymer
or of the added monomer and comonomers to copolymer is achieved in
the first reactor, compared to the downstream reactors.
[0048] In loop reactors, the polymerization mixture is pumped
continuously through a cyclic reactor tube. As a result of the
pumped circulation, continual mixing of the reaction mixture is
achieved and the catalyst introduced and the monomers fed in are
distributed in the reaction mixture. Furthermore, the pumped
circulation prevents sedimentation of the suspended polymer. The
removal of the heat of reaction via the reactor wall is also
promoted by the pumped circulation. In general, these reactors
consist essentially of a cyclic reactor tube having one or more
ascending legs and one or more descending legs which are enclosed
by cooling jackets for removal of the heat of reaction and also
horizontal tube sections which connect the vertical legs. The
impeller pump, the catalyst feed facilities and the monomer feed
facilities and also the discharge facility, thus in general the
settling legs, are usually installed in the lower tube section.
However, the reactor can also have more than two vertical tube
sections, so that a meandering arrangement is obtained.
[0049] The polymer is generally discharged continuously from the
loop reactor via settling legs. These settling legs are vertical
attachments which branch off from the lower reactor tube section
and in which the polymer particles can sediment. After
sedimentation of the polymer has occurred to a particular degree, a
valve at the lower end of the settling legs is briefly opened and
the sedimented polymer is discharged discontinuously.
[0050] In a preferred embodiment, the suspension polymerization is
carried out in a loop reactor at an ethylene concentration of at
least 10 mol %, preferably 15 mol %, particularly preferably 17 mol
%, based on the suspension medium. For the purpose of these
figures, the suspension medium is not the input suspension medium
such as isobutane alone but rather the mixture of this input
suspension medium with the monomers dissolved therein. The ethylene
concentration can easily be determined by gas-chromatographic
analysis of the suspension medium.
[0051] A preferred polymerization process is that carried out in a
horizontally or vertically stirred or fluidized gas phase.
[0052] Particular preference is given to gas-phase polymerization
in a fluidized-bed reactor, in which the circulated reactor gas is
fed in at the lower end of a reactor and is taken off again at its
upper end. When such a process is employed for the polymerization
of 1-olefins, the circulated reactor gas is usually a mixture of
the 1-olefin to be polymerized, if desired a molecular weight
regulator such as hydrogen and inert gases such as nitrogen and/or
lower alkanes such as ethane, propane, butane, pentane or hexane.
The velocity of the reactor gas has to be sufficiently high firstly
to fluidize the mixed bed of finely divided polymer serving as
polymerization zone in the tube and secondly to remove the heat of
polymerization effectively (noncondensed mode). The polymerization
can also be carried out in the condensed or supercondensed mode, in
which part of the circulating gas is cooled to below the dew point
and returned to the reactor together as a two-phase mixture or
separately as a liquid and a gas phase in order to make additional
use of the enthalpy of vaporization for cooling the reaction
gas.
[0053] In gas-phase fluidized-bed reactors, it is advisable to work
at pressures of from 0.1 to 10 MPa, preferably from 0.5 to 8 MPa
and in particular from 1.0 to 3 MPa. In addition, the cooling
capacity depends on the temperature at which the (co)polymerization
in the fluidized bed is carried out. The process is advantageously
carried out at temperatures of from 30 to 160.degree. C.,
particularly preferably from 65 to 125.degree. C., with
temperatures in the upper part of this range being preferred for
copolymers of relatively high density and temperatures in the lower
part of this range being preferred for copolymers of lower
density.
[0054] It is also possible to use a multizone reactor in which two
polymerization zones are linked to one another and the polymer is
passed alternately a plurality of times through these two zones,
with the two zones also being able to have different polymerization
conditions. Such a reactor is described, for example, in WO
97/04015 and WO 00/02929.
[0055] The different or else identical polymerization processes can
also optionally be connected to one another in series and thus form
a polymerization cascade. It is also possible to operate the
reactor using two or more identical or different processes.
However, the polymerization is preferably carried out in only a
single reactor.
[0056] All documents mentioned are expressly incorporated by
reference into the present patent application. All proportions and
ratios in the present patent application are by weight based on the
total weight of the corresponding mixtures, unless indicated
otherwise.
[0057] The invention is illustrated below with the aid of an
example, without being restricted thereto.
EXAMPLE
[0058] A conductivity measurement sensor from Yokogawa, special
model S250155C J5-17 was used. The conductivity measurement sensor
1 had a measurement cell 2 (Yokogawa, model SX42-SX34-DF) having 2
stainless steel electrodes and an integrated Pt100 temperature
sensor. The system cell constant is 0.01005 cm.sup.-1 and the
measurement range is 0-0.200 .mu.S/cm. The flow valve is from
Yokogawa, model FF40S22.
[0059] The measurement solution, which had been brought to the
appropriate temperature in a double-walled vessel, could be fed
into the conductivity measurement sensor 2 by means of a magnetic
centrifugal pump 3 (IWAKI MD 6, pumping rate: 8 l/min). The
measurement sensor was connected to a processing unit which
displayed the temperature and conductivity.
[0060] 500 ml of purified n-hexane were placed in the apparatus
under protective gas and brought to a temperature of 20.degree. C.
The antistatic Costelan AS 100 (from Costenoble, Eschborn, Germany)
was then added a little at a time and, after sufficient mixing and
constancy of the temperature, the conductivity value was read off.
To monitor the concentration, the solution was subsequently diluted
with a defined volume of n-hexane and the conductivity was read
off. Between the experiments, the measurement solution was drained
and the apparatus was rinsed a number of times with n-hexane.
[0061] All measurements were carried out at a temperature of
20.degree. C. The results are shown in Table 1.
TABLE-US-00001 TABLE 1 Concentration of Costelan Conductivity [% by
weight] [.mu.S/cm] 0.000 0.000 0.032 0.003 0.061 0.004 0.095 0.007
0.111 0.008 0.129 0.009 0.146 0.010 0.160 0.011 0.175 0.012 0.191
0.013 0.207 0.014 0.223 0.015 0.239 0.016 0.257 0.017 0.276 0.018
0.297 0.019 0.316 0.020 0.335 0.021 0.573 0.034 0.842 0.047 1.124
0.061
[0062] A linear dependence of the conductivity on the concentration
is obtained.
[0063] The series of experiments using different concentrations of
Costelan AS100 shows that this measurement principle is very
readily able to react sensitively to the changes in the
concentration and thus ensure an accurate measurement. Such a
conductivity measurement sensor can be installed without problems
in all lines of a polymerization plant.
* * * * *